An electronic device and methods for inductively charging an electronic device using another external electronic device. User input defining a form that has one or more fields is received. The sample and reference light is guided from the sample location to the evaluating device in a common fibre. The forgery-proof electronic signature makes a secure data transfer possible. The insert is rectilinear, and the recess for the insert in the metallic body forms a rectilinear groove, the cover being dimensioned so as to be able to placed on the insert in the recess after having been shrunk by cooling and to establish a tight fit in the groove by dilation such as to close the space. The printer identifies an optical characteristic of the mixed ink and compares it to the optical characteristic for black ink.